While \(\alpha _{\rm ox}\)  measures the relative strength of QSO emission in the UV and X-ray bands, the X-ray bolometric correction (\(K_{bol}=\frac{L_{bol}}{L_X}\) ) measures the fraction of bolometric power emitted in the X-ray band. \(\alpha _{\rm ox}\)  and \(K_{bol}\)  are clearly related: steeper values of \(\alpha _{\rm ox}\)  correspond to higher values of \(K_{bol}\) , as the
contribution of the X-ray emission to the bolometric QSO luminosity decreases, and the QSO total power is increasingly dominated by the optical/UV band.
Fig. REF  presents the \(L_X-L_{bol}\)  plane for QSOs. The relation between \(L_x\)  and \(L_{bol}\)  flattens at increasing bolometric luminosity (e.g., [1]}), such that larger values of \(K_{bol}\)  are measured for more luminous QSOs. High-redshift QSOs are consistent with this general trend, once again implying that the accretion physics in QSOs changes with increasing luminosity, thus possibly Eddington ratio, but does not depend strongly on redshift, at least for what the disc-corona coupling is concerned. However, an important caveat regarding high-redshift QSOs is needed here: the spectral energy distributions (SEDs) of these systems is poorly sampled, and usually only a few rest-frame UV photometric points are available, in contrast to low-redshift QSOs. Therefore, for the vast majority of these objects, \(L_{bol}\)  is estimated by applying UV bolometric corrections (e.g., [2]}), which have been calibrated at low redshift. Therefore, for high-redshift QSOs, the \(L_X-L_{bol}\)  relation is mostly a byproduct of the \(\alpha _{\rm ox}-L_{UV}\)  anti-correlation.
